The present inventions relates to motor driven servoactuators of the type operated by a low voltage direct current motor and employing a speed reducer to provide high torque slow rate of rotation output. Servoactuators of this type are known to employ a feedback potentiometer coupled to rotate with the output member for providing a variable resistance signal proportional to the rotational position of the output member. An example of such a device is a servoactuator employed for automative passenger compartment temperature control systems, one such device being shown and described in U.S. Pat. No. 4,616,164. The servoactuator in the aforesaid '164 patent employs a variable resistance strip on a portion of the housing with an electrical wiper contact rotated thereagainst by the output member for providing an electrical resistance signal proportional to the rotational position of the output member.
In providing electric servoactuators having a slow rate of rotation output and high torque output for automotive applications, it has been found necessary to employ a low current high RPM drive motor to accommodate the on-board vehicle low voltage power supply, typically 12 volts, and to provide a numerically high-ratio speed reduction in order to provide the desired output torque and position resolution. In order to achieve a numerically high-ratio speed reduction, several stages of gearing have been required to accomodate the high motor shaft RPM at the input stage of the speed reducer; and, this combination has resulted in prohibitive levels of vibration and noise transmitted to the vehicle passenger compartment through the servoactuator and motor housing.
Furthermore, in order to calibrate the output member position sensing feedback potentiometer, it has been required to position the output member at a specified position and then assemble the potentiometer to the speed reducer gearing in order to insure that the potentiometer is properly calibrated for the output member position with respect to the full scale output of the potentiometer. This has resulted in complicated and costly manufacturing procedures and difficulties in calibrating the servoactuator in high volume production operations.
Therefore, it has been desired to provide a low cost and compact low voltage d.c. motor-operated servoactuator having a numerically high-ratio speed reduction between the motor and the output member and to provide such a servoactuator that is easily manufactured, assembled and calibrated in high volume production and with minimum manufacturing cost.